The present invention relates to a lead frame transfer apparatus used in a semiconductor production line.
In the case of the production of the semiconductor devices, after the completion of the wafer process, in order to draw electrodes on a semiconductor chip and connect them to leads of a package, a die bonding process for bonding a semiconductor chip to a lead frame, a wire bonding process for connecting and the electrodes on the semiconductor chip to the leads of a lead frame and a resin molding process for sealing the semiconductor chip with a resin to form a package are carried out. In each process and between processes, a lead frame is handled as a unit part so that transfer thereof is one of the very important matters in the production of semiconductor devices.
Depending upon the shapes, the number of pins and other factors of semiconductor devices, various types of lead frames exist. Since a plurality of semiconductor chips are mounted on each lead frame, the widths of the lead frames are standardized in order that the storage and transfer of the lead frames may be facilitated. But some of the lead frames have different widths, respectively. Therefore lead frame transfer apparatuses can preferably vary their width as needs demand.
FIG. 1 is a perspective view of a conventional frame transfer apparatus which is used, for instance, in the wire bonding stage. Lead frames 1, upon each of which a plurality of semiconductor chips 2 are mounted, are stored in a lead frame magazine 32. The lead frames 2 are pulled out of the lead frame magazine 32 by a feed pawl 42 one at a time and are placed between guide rails 4 and 5 and then transferred by another feel pawl 43 so as to be stored into an empty frame magazine 33 disposed at the other ends of the guide rails 4 and 5 remote from the storage magazine 32 after completion of wire bonding. The frame magazines 32 and 33 are equipped with magazine elevators 34 and 35, respectively, which in turn are engaged with lead screws 38 and 39 rotated by motors 30 and 31 so that the elevators 34 and 35 are vertically displaced along sliding shafts 36 and 40 and the sliding shafts 37 and 41, respectively.
In the vicinity of the mid-point of the guide rail pair 4 and 5 between the lengthwise ends, a wire bonder 45 is disposed. Its arm 45b is operated so that a wire 45a is fed so as to electrically interconnect each electrode on the semiconductor chip 2 and a corresponding lead on the lead frame 1.
FIG. 2 is a sectional view taken along the line A--A of FIG. 1. The guide rails 4 and 5 are provided on the upper surface of a base 21 with bolts 22 and nuts 23 in such a way that the guide rails 4 and 5 are slidable in the widthwise direction of the lead frame 1 if the bolts are loosened. Side edges of the lead frame 1 upon which the semiconductor chips 2 are mounted are inserted into and supported by grooves 4b and 5b which are formed by a cut-out portion 4a (5a) cut out on the inner side of the top surface of the guide rail 4 (5) and a cover plate 4c (5c). A heater block 3 for heating the lead frame 1 during the wire bonding operation is disposed substantially at the mid-point between the guide rails 4 and 5.
In the case of the lead frame transfer apparatus of the type described above, the width L between the guide rails 4 and 5 must be so adjusted that the width between the grooves 4b and 5b becomes slightly wider than the width of the lead frame 1. Thus in the case of the adjustment of the width L, a troublesome and time-consuming manual operation of loosening the bolts 22 and nuts 23 is required in order to place the guide rail 4 and 5 at their predetermined position. Moreover, as a result, during the widthwise adjustment, the production line is stopped. Generally speaking, the shorter the adjustment time interval, the higher the operational efficiency of the production line becomes. From this point of view, the shut-down time interval of the production line due to the adjustment of the width L between the guide rails 4 and 5 cannot be neglected, because as described above, the widths of the lead frames 1 vary over a wide range. One of the measures for shortening the width adjustment time interval is to place a rail width gauge 24 between the guide rails as shown in FIG. 2. However, when such a gauge 24 is used, the production line is shut down for tens of minutes for each width adjustment operation. Especially, since there is a current trend in which many types of semiconductor devices are respectively produced with a small quantity, there arises a problem that the number of width adjustment operations is increased.
In view of the above, the same inventor proposed a lead frame transfer apparatus which is disclosed in detail in Japanese Laid-Open Patent Application No. 59-172631, so that the width between the guide rails can be automatically varied in response to types of lead frames.
However, even with such automatic width adjustment apparatus, there often arises a problem in which the transfer of the lead frame 1 becomes impossible because of the thermal expansion of the lead frame heated by the heater block 3 so that its side edges are brought into contact with the bottoms of the grooves 4b and 5b of the guide rails 4 and 5. A further problem is such that during attaching the lead frame 1 to guide rails, deformation or bending of the lead frame occurs, resulting in the break of a wire connection. A yet further problem is such that because of the tolerances in the width of the lead frames 1 defined by the same standard, if the guide rail width L is adjusted for the width of a certain lead frame 1, some other lead frames may be deformed.
As described above, the conventional lead frame transfer apparatuses have the problems that a long time interval is required for the adjustment of the width between the guide rails and that deformations of the lead frames and wire breaks occur due to the thermal expansion of the lead frame and tolerances in size after the guide rail width adjustment.